Split big image with python. You can split with split_image.py, assemble with assemble_image.py

assemble_image.py

# assemble images which is splited by split_image.py

import cv2
import glob
import os
import tqdm
import numpy as np
from itertools import islice
from multiprocessing import Pool

path = r'/path/to/common_dir/of/common_dirnames'
common_dirnames = [ # assemble 'common_dir_0_0', 'common_dir_0_1', 'common_dir_1_0', 'common_dir_1_1' into 'common_dir_assemble'
    'common_dir'
]
split_img_amount = (2, 2) # Height, Width

def merge_image(_files):
    assemble_dir = _files[1]
    _files = _files[0]
    if len(set(map(os.path.basename, _files))) != 1:
        raise ValueError('Image names are mismatched {}'.format(set(map(os.path.basename, _files))))
    split_imges = [[cv2.imread(_files[i * split_img_amount[1] + j], cv2.IMREAD_UNCHANGED) for j in range(split_img_amount[1])] for i in range(split_img_amount[0])]
    img = []
    for split_img in split_imges:
        img.append(np.concatenate(split_img, axis=1))
    img = np.concatenate(img, axis=0)
    cv2.imwrite(os.path.join(path, assemble_dir, os.path.basename(_files[0])), img)

if __name__ == '__main__':
    num_process = 16
    split_files = []
    for common_dir in common_dirnames:
        assemble_dir = '{}_assemble'.format(common_dir)
        split_dir = [['{}_{}_{}'.format(common_dir, i, j) for j in range(split_img_amount[1])] for i in range(split_img_amount[0])]
        os.mkdir(os.path.join(path, assemble_dir))
        temp_split_files = [sorted(glob.glob(os.path.join(path, temp_dir, '*.png'), recursive=True)) for dir_list in split_dir for temp_dir in dir_list]
        temp_split_files = list(zip(*temp_split_files))
        split_files += [(zipped_file, assemble_dir) for zipped_file in temp_split_files]
    with Pool(processes=num_process) as p:
        r = list(tqdm.tqdm(p.imap(merge_image, split_files), total=len(split_files)))
 

split_image.py

import cv2
import glob
import os
import tqdm
from itertools import islice
from multiprocessing import Pool
from pathlib import Path

path = r'path/to/file/COMMON_DIR/*.png'
split_img_amount = (2, 2) # Height, Width
split_dir = [['_{}_{}'.format(i, j) for j in range(split_img_amount[1])] for i in range(split_img_amount[0])]

def split_image(_file):
    img = cv2.imread(_file, cv2.IMREAD_UNCHANGED)
    if img.shape[0] % split_img_amount[0] != 0 or img.shape[1] % split_img_amount[1] != 0:
        raise ValueError('Image resolution is not the multiple of number of split image')
    stride = (img.shape[0] // split_img_amount[0], img.shape[1] // split_img_amount[1])
    for i in range(split_img_amount[0]):
        for j in range(split_img_amount[1]):
            split_img = img[i * stride[0]:(i + 1) * stride[0],j * stride[1]:(j + 1) * stride[1],:]
            dirname = os.path.dirname(_file)
            save_path = os.path.join(os.path.dirname(dirname), os.path.basename(dirname) + split_dir[i][j], os.path.basename(_file))
            Path(os.path.dirname(save_path)).mkdir(parents=True, exist_ok=True)
            cv2.imwrite(save_path, split_img)

if __name__ == '__main__':
    num_process = 16
    files = glob.glob(path, recursive=True)
    # iter_files = iter(files)
    # files = [list(islice(iter_files, e)) for e in [len(files) // num_process] * (num_process + 1)]
    with Pool(processes=num_process) as p:
        r = list(tqdm.tqdm(p.imap(split_image, files), total=len(files)))